German Patent Application No. DE 101 36 183, for example, describes a method for testing the functionality of a tank venting valve located in a fuel tank system of a motor vehicle in particular.
In this method, a defective tank venting valve is diagnosed by analyzing at least one operating variable, e.g., the pump current of at least one pressure source, a pump for example.
In this method, the tank venting valve is initially closed while the activated carbon filter shut-off valve is closed and the pump is subsequently operated for building up a preferable overpressure in the tank. The overpressure build-up is measurable based on the pump's operating variable. The pressure rapidly drops again during subsequent opening of the tank venting valve. This may also be detected based on the operating variable.
On the basis of the operating variable, it is assumed that the tank venting valve is intact or defective.
On the basis of this method, testing of the tank venting valve's functionality may be effectively carried out. However, a defective connection between the tank venting valve and the intake manifold of the engine is not able to be detected.
Due to statutory provisions in many countries, it is now required to test not only the functionality of the tank venting valve but also the functionality of the connection between the tank venting valve and the intake manifold of the engine. In other words, it must be ensured that a purge flow exists via the tank venting valve to the engine.
It is therefore an object of the present invention to provide a method for testing the functionality of a tank venting system of a motor vehicle having an internal combustion engine in such a way that both the functionality of the tank venting valve and the functionality of the purge process may be tested.